1. Field of the Invention
The present invention relates to an apparatus and method for controlling the brightness level of a display, and more particularly, to an apparatus and method for controlling the brightness level of a liquid crystal display in an electronic device such as a notebook computer.
2. Description of the Related Art
Generally, a notebook computer providing a portable convenience is provided with a liquid crystal display (LCD) integrally constructed with a main body. The LCDs can be fabricated or produced in various kinds and sizes according to manufacturers.
FIG. 1 is a block diagram of a general computer system provided with an LCD coupled thereto.
As shown in FIG. 1, an inverter power is supplied to the LCD through an inverter cable under the control of a microprocessor. The brightness of the LCD is controlled regardless of manufacturer or the LCD's characteristics.
LCDs manufactured by different suppliers have different sizes and have different inherent optical characteristics. In a conventional LCD a cold cathode fluorescent lamp (CCFL) device is provided at an upper side or a lower side as a light emitting device. The CCFL device emits light in response to a high voltage applied through the inverter, which controls the brightness of the LCD.
The CCFL devices also have different inherent optical characteristics according to the manufacturers. However, the manufacturers producing notebook computers use the same inverter to operate all CCFL devices equipped in various LCDs, regardless of the particular characteristics of the CCFL devices.
Because the LCDs and the CCFL devices have different inherent optical characteristics, although an equal level of power is applied to the CCFL devices by the use of the same inverter, the brightness levels are different depending on the individual device characteristics.
Even when the LCDs and the CCFL devices are manufactured by a single manufacturer, and even though they employ the same inverter, the brightness levels of the LCDs may be different because of small differences between individual devices.
In order to solve the aforementioned problems and maintain the brightness of the LCDs at a constant level, the power applied to the CCFL device through the inverter is set based on the assumption that the LCD has relatively bad optical characteristics. In this case, an LCD having relatively good optical characteristics will operate at an unnecessarily high brightness level. This wastes battery power, and can dazzle a user's eye.
For instance, when it is assumed that in notebook computers using the same inverter, the appropriate brightness level is 30 nit (Cd/m2), an LCD #A having relatively bad optical characteristics needs 2 Watts of power to maintain the brightness level at 30 nit. However, an LCD #B having a relatively good optical characteristics needs only 1.5 Watts of power. In spite of the above fact, the manufacturers set the consumption power applied to both LCD #A and LCD #B at 2 Watts to ensure that all computers will output 30 nit. Because of this, the LCD #B wastes the power of 0.5 Watts ineffectively, and too bright a picture is outputted on the screen of computer #B.